The invention relates to a power miter saw or slide compound miter saw for use in carpentry and other cutting crafts. More particularly, the invention relates to a linkage arrangement that will automatically align a movable blade guard, allow free rotation of the blade guard to a non-surround position, and provide a lock-out which prevents effective use of the cutting unit when the blade guard has been moved to the non-surround position.
Power miter saws and power slide compound miter saws have been used as a quick and efficient way of making angular cuts in a work piece, usually a portion of a chair rail, baseboard, crown molding or aluminum siding. An angle cut is necessary to form a mating joint with a similar piece of wood having a mating surface comprised of an opposing angle face complimentary to that of the mated work piece. Typically, these joints are found at the corners of the room, doors and windows. The angle required varies according to the shape of the room and other requirements particular to the application.
Power miter saws and the like typically have a base with a turntable mounted thereon. A cutting unit is mounted on the turntable for movement between cutting and non-cutting positions and includes an electric motor supporting a circular saw blade. The combination of the motor and saw blade is typically housed in the cutting unit. The cutting unit housing covers approximately the upper half of the circular saw blade leaving the lower half of the blade exposed.
A lower blade guard is normally provided which protects or covers an optimum amount of the lower half of the circular saw blade. It is knoll in the art to provide a movable lower blade guard with an actuating mechanism so that when the cutting unit is in the at rest, non-cutting position, the movable blade guard is in a surround position covering the saw blade. As the cutting unit is moved to a cutting position, the movable blade guard rotates from the surround position to a non-surround position to allow the saw blade to contact and cut a work piece. To achieve this operation the lower movable blade guard must be precisely adjusted to the optimum surround position relative to the lower half of the blade. Because the upper and lower blade guards, in combination, substantially cover the saw blade, provision is made to allow the movable lower blade guard to be manually movable to a non-surround position to allow replacement or changing of the blade.
The prior art recognizes that it is desirable to prevent unintentional manual movement of the movable guard to the non-surround position and it is known to provide some type of guard locking arrangement that must be released before the movable guard can be moved to the non-surround position. Such locking arrangements frequently require the use of a separate tool in order to effect the unlocking. Users prefer that there be no locking arrangement so that the guard is free to be moved to a non-surround position without going through an unlocking procedure. However, if the guard design permits such free guard movement the cutting unit can be moved to a cutting position without returning the guard to a blade surrounding position. In addition if the movable blade guard is freely movable, the guard could be permanently secured in the non-surround position.
Another problem exists in assembling the movable guard and its actuating mechanism on the cutting unit. In the assembly of miter saws careful setting of the movable guard to an optimum surround position is manually made by the assembler. In addition, the actuating mechanism for the blade guard must also be manually set for proper guard raising action. Because these two settings are interrelated the making of one setting frequently alters the other setting thus requiring it to be reset. The set and reset alignment procedure is time consuming, increases the cost of assembly, and can result in the saw being initially assembled with improper settings which increases the cost of inspection and quality control.
In summary, the problem that exists is how to provide a simple low cost, rugged guard arrangement that will allow the desired free manual movement of the miter saw blade movable guard to a non-surround position, and which will automatically prevent the cutting unit from being moved to a cutting position while the movable guard is in the non-surround position. In addition, known guard arrangements do not address the assembly alignment setting problems and there is a need for guard arrangement that will enable an assembler to make one simple alignment setting that simultaneously places the movable blade guard at an optimum surround position and also sets the guard actuating linkage for proper operation.
U.S. Pat. No. 5,054,352, issued to Fushiya et al., illustrates a power miter saw including a lower blade guard movable from a surround position to a non-surround position. The lower blade guard is freely movable in that it does not include a locking means which must be released before the blade guard can be rotated from its surround position to its non-surround position. The Fushiya et al. miter saw does not include an arrangement which prevents lowering of the cutting unit when the lower blade guard is in the non-surround position.
U.S. Pat. No. 4,934,233, issued to Brundage et al., shows a power miter saw including a swinging lower blade guard for covering the lower, or cutting portion of the circular saw blade. In order to rotate the lower blade guard to the non-surround position and expose the blade for removal, a threaded fastener must first be loosened.
U.S. Pat. No. 4,805,504, issued to Fushiya et al., illustrates a power miter saw having an actuating means disposed between the cutting unit and the lower blade guard for directly associating the movement of the lower blade guard with pivotable movement of the cutting unit. An engaging pin must first be released to allow the actuating means to rotate allowing movement of the lower blade guard.
U.S. Pat. No. 4,774,866, issued to Dehari et al., shows a saw blade guard arrangement in an electrically power miter saw. The linkage arrangement supporting the lower blade guard for pivotal movement from a surround position to a non-surround position allows for free manual movement of the blade guard. The Dehari et al. miter saw also includes an apparatus for adjusting the position of the saw arm and, as a result, the position of the lower blade guard, but does not include a linkage arrangement that locks the cutting unit in the non-cutting position when the blade guard is in the non-surround position.
U.S. Pat. No. 4,581,966, issued to Kaiser et al., illustrates a power miter saw including a linkage system for mounting the lower blade guard for movement from a surround position to a non-surround position. To accommodate changing of the saw blade, a pivot bolt must be partially withdrawn using conventional hand tools to unlock the linkage arrangement and free the blade guard for pivotal movement. The pivot bolt has a head which prevents the cutting unit from being lowered to its cutting position until the lever has been returned to its normal position and the pivot bolt is put back into place.
U.S. Pat. No. 4,343,213, issued to Drixler, shows a power miter saw having a lower blade guard adapted to move from a surround position to a non-surround position. The lower blade guard assembly includes a cam-following roller 78 which engages a recess 76 to compulsorily lock the lower blade guard in its maximum cover position when the cutting unit is in the raised at rest position, but does not include an arrangement allowing free movement of the lower blade guard when the cutting unit is in the at rest position.
Attention is also directed to the following U.S. Patents which further show the state of the art in saw blade guard assemblies.
______________________________________ U.S. Pat. No. 5,042,348 Brundage et al. 8/27/91 U.S. Pat. No. 5,020,406 Sasaki et al. 6/4/91 U.S. Pat. No. 4,869,142 Sato et al. 9/26/89 U.S. Pat. No. 4,799,416 Kumasaka et al. 1/24/89 U.S. Pat. No. 4,532,841 Stackhouse, Jr. 8/6/85 U.S. Pat. No. 3,998,121 Bennett 12/21/76 U.S. Pat. No. 3,922,785 Fushiya 12/2/75 U.S. Pat. No. 3,913,437 Speer et al. 10/21/75 U.S. Pat. No. 3,787,973 Beisch et al. 1/29/74 U.S. Pat. No. 3,730,239 Kaman et al. 5/1/73 U.S. Pat. No. 3,706,332 George 12/19/72 ______________________________________